This invention relates to the collection from surfaces of samples of trace particles or liquids, or other compounds, and vapours thereof, for chemical detection by various analytical means, such as an ion mobility spectrometer (IMS), gas chromatography (GC), liquid chromatography (LC), mass spectrometry (MS) and other methods, the compounds being present either as traces within particles or as discrete particles or aerosols, droplets or the like, or as vapours. The invention more particularly relates to the detection of explosives, narcotics, and other contraband concealed by individuals in their belongings or in transported goods and cargo, or in vehicles and aircraft. However, the invention also encompasses environmental sampling such as chemical warfare agent liquid droplets and aerosols which are extremely toxic and for which no hand contact can be tolerated.
The removal of dust as a simple household task from domestic dwellings has been and is still carried out with dust cloths. In more sophisticated situations, chatelaines and housekeepers have employed maids, butlers and valets equipped with white gloves or mittens to remove dust, polish silverware and furniture. Previously, there has been no necessity or interest in analyzing the collected dust particles. Rather, the sole intent was to collect and throw out dust and dirt particles.
The necessity to collect dust and particles for analysis is a more recent requirement. With the advent of terrorism where explosives can be concealed to create undetectable bombs and also with drug smugglers concealing their drug shipments, the need for trace/forensic detection has become necessary. While early explosives detectors relied on the collection of atmospheric explosives vapours, modern high power explosives are plastic with extremely low vapour pressures thereby presenting vapour detection instruments with extremely difficult detection situations to the point of impossibility. Modern plastic explosives can have vapour pressures 5 or 6 orders of magnitude lower than the traditional volatile explosives such as nitroglycerine (NG), trinitrotoluene (TNT) and ethylene glycol denitrate (EGDN). For example, U.S. Pat. No. 4,909,090 teaches the use of hand operated vapour samplers which heats the surface to assist in dislodging vapours which are trapped on collector surfaces in the probe. However, with the very low vapour pressure of plastic explosives and drugs this method is extremely limited in its usefulness. Drugs like cocaine, heroine and others also have very low vapour pressures and thus are undetectable by existing vapour detection instruments.
Modern detection equipment can detect extremely low levels of explosives, narcotics and the like, in the range of nanograms or picograms. However, this simply raises the problem of obtaining a suitable sample. Accordingly, rather than attempt to collect a vapour sample, an alternative approach of particle collection and analysis was proposed, notably by Barringer, et al, and followed by others, both for forensics purposes as well as for surface geochemical exploration where trace metals and organometals can be useful as pathfinder indicators in mineral exploration activities. Earlier patents have covered these applications, such as Barringer U.S. Pat. Nos. 3,970,428; 4,220,414; 4,192,176; and 5,425,263.
Particle collection techniques include: surface inspection by means of physical particle collection in minute amounts; the use of dust pan-brush arrangements; vacuum suction onto porous or semi-porous substrates, filters, membranes and the like; the use of swabs, swipes, gloves, etc. One such method is described in U.S. Pat. No. 5,476,794 which describes the removal of particles with a glove and the use of an intermediate step, that of vacuum suction off the glove. Applicant""s own earlier U.S. Pat. No. 5,425,263 discloses an apparatus and method for collecting a sample of particles or droplets, or a substrate, for analysis in an IMS device or the like. These techniques have been the subject of earlier patents, which have developed into more sophisticated techniques incorporated into various instrumental devices for direct analysis, including plasma optical emission spectrometers, optical analyzers and mass spectrometers among others.
Gloves, mitts and swipes have been used in various forms for particle collection. Disadvantages exist with these earlier systems of collection. The major disadvantage of most of these earlier techniques is that an intermediate step is required to transfer from such a glove or the like any particles/trace chemicals so collected for presentation to the analytical device. One method is to use a suction device to vacuum the glove or mitt, as in U.S. Pat. No. 5,476,794.
Applicant""s earlier U.S. Pat. No. 5,859,375 was intended to overcome many of the problems in this art, relating to collection of particles/vapours. It provided a technique for quickly and simply collecting a sample directly onto a substrate, while eliminating, or at least significantly reducing, the problems of cross-contamination between a sample or contamination of a user""s hands.
However, in this earlier technique, there was no way of collecting just a vapour sample. Some substances of interest have a significant vapour pressure at ambient temperatures, yet are difficult to collect as particles and/or droplets.
The surfaces of objects which are contaminated with explosives, drugs, or other chemicals, frequently retain traces of these substances in the form of small particles, and, if the substances in question have an appreciable vapour pressure, the objects evolve small amounts of chemical vapour. If the surfaces of such objects are swabbed with a suitably chosen material, as in the patents mentioned above, some of the particles will adhere to the swab.
Similarly, if a sample of air is aspirated from close to the surface of the object, through a cartridge containing an appropriate sorbent, some of the vapour of the target chemicals will be retained. The chemicals can then be detected by inserting the swab and the cartridge into suitable analytical apparatus, such as an Ion Mobility Spectrometer (IMS) equipped with a pyrolyser/desorber. Collecting both particles and vapour extends the range of compounds which can be detected, increases the probability of detection, and reduces the false alarm rate. The circumstances in which objects are to be screened for concealed contraband, such as drugs or explosives, dictate that the objects be processed rapidly, and also that samples be obtained from interior surfaces of vehicles and other large structures. The present invention addresses these needs by providing a device which combines both sampling modalities in a unit which can be carried and operated with one hand. It has the further advantage that it may be configured to have extended length and minimal diameter, extending the effective reach of the operator into otherwise inaccessible or dangerous or contaminated areas.
Techniques that rely on particle collection by vacuum suction and the like require a high air flow rate to efficiently dislodge particles from a surface, so that a collector using this method is larger, heavier, and less convenient to use than the present invention. U.S. Pat. No. 3,925,022 teaches the use of an absorbent to pre-concentrate vapours prior to detection, but the apparatus described is integral with the analyzer used for detection and not portable, nor does it provide collection of particles. U.S. Pat. No. 5,753,832 describes an apparatus for collection of both particles and vapour, but uses a single conduit and airflow. Since the optimum air flows for particle and vapour collection are very different, this apparatus must use an airflow rate which is a compromise, resulting in reduced collection efficiency for at least one of the phases. In addition, it requires an umbilical hose connection from the sampling point to the analyzer. This makes use more difficult, and also is subject to loss of both particle and vapour by adhesion to the walls of the hose, leading to loss of detection sensitivity, and to false alarms following a genuine detection, due to release of target analyte trapped on the walls of the hose.
In accordance with the present invention, there is provided a method of collecting a sample of a substance of interest, the method comprising the steps of:
(1) providing an apparatus having means for collecting a vapour sample and retaining means for retaining a substrate;
(2) providing a substrate having a working portion and a mounting portion, and mounting the substrate by the mounting portion of the substrate, whereby the working portion of the substrate is exposed for use;
(3) manipulating the apparatus so that the working portion of the substrate traverses surfaces of interest;
(4) operating the vapour sampling means to obtain a vapour sample; and
(5) analyzing the vapour sample collected by the vapour sampling means and a particulate sample collected on the substrate.
The method preferably includes providing the vapour sampling means with a cartridge including an absorbent material adapted to absorb a vapour sample from air flow therethrough, and step (4) then comprises passing air through the cartridge to generate a vapour sample on the absorbent material within the cartridge.
More preferably, step (5) comprises, for the substrate, releasing the substrate from the retaining means, mounting the substrate in an analyzer and causing particulates on the substrate to be released and/or desorbed, and for the vapour sample, the method comprising removing the cartridge from the sampling apparatus, mounting the cartridge in an analyzer, and causing the vapour samples to be released from the absorbent material.
Advantageously, for the particulate sample, the substrate is mounted in an analyzer and heated to cause desorption of vapours from particulates on the substrate, and for the vapour sample, the cartridge is heated to cause desorption of the vapour sample from the absorbent material.
The method can be applied to the detection of at least one of drugs, explosives, chemical warfare agents and biological warfare agents. For example, the can be applied to detecting at least one of drugs, explosives, ICAO taggants for explosives, chemical warfare agents, chemical warfare agent precursors, biological warfare agents and the like.
Preferably, the method includes controlling the vapour sampling means, whereby the flow rate of air and the duration of a sampling is sufficient to ensure the collection of a sufficient amount of vapour sample on the absorbent material.